Study finds strong link between night-time light exposure and stroke risk

A group of researchers from Zhejiang University in China carried out an extensive study involving nearly 30,000 individuals. Their analysis indicates a significant link between high exposure to artificial and bright light at night and an enhanced risk of severe cerebrovascular incidents. Additionally, the study reveals that air pollution might pose similar health risks.

Bright outdoor lighting, aimed at improving night-time visibility, enhances safety and comfort for individuals. However, the research team suggests that there is an excessive use of such lighting currently. Consequently, around 80% of the population resides in areas affected by light pollution, which negatively impacts human health.

Prior research has shown a correlation between high exposure to artificial light at night and the onset of cardiovascular diseases. It now seems that light pollution could also be a risk factor for brain health.

Dr. Jian-Bing Wang, a lead author of the study, highlights that the world has achieved substantial progress in reducing conventional cardiovascular risk factors, like smoking, obesity, and type 2 diabetes. Nevertheless, he stresses the importance of addressing environmental factors in the ongoing effort to lessen the global disease burden.

The study reviewed the cases of over 28,000 adults in China. Using satellite imagery, Dr. Wang's team produced a light pollution map, which helped in estimating the exposure of urban dwellers to night-time light from outdoor sources. This information was then correlated with hospital records and death certificates confirming stroke incidents. The study spanned six years and considered light from sources such as fluorescent, incandescent, and LED lamps.

Findings reveal that, during this period, 1,278 individuals were diagnosed with cerebrovascular disease, including 777 cases of ischemic stroke and 133 cases of hemorrhagic stroke. Those most exposed to night-time lights were 43% more likely to suffer from cerebrovascular diseases compared to those experiencing the least exposure.

The research also highlights that individuals with the highest exposure to suspended particulate matter PM2.5, primarily from the combustion of gasoline, diesel, or wood, had a 41% increased risk of cerebrovascular incidents. PM10 particles, mostly from dust and smoke, raised the stroke risk by 50%.

Furthermore, those with the most significant exposure to nitrogen oxide faced a 31% greater risk of developing cerebrovascular diseases than those least exposed.

"Our findings suggest that high levels of night-time exposure to external artificial light could be a risk factor for cerebrovascular diseases," Dr. Wang notes.

"Hence, particularly for urban residents, we recommend considering ways to reduce such exposure to mitigate its potential harmful effects," he advises.

The authors explain that the correlation they observed might be attributed to the continuous night-time exposure to bright light inhibiting melatonin production. Melatonin is a sleep-promoting hormone, and its suppression disturbs our 24-hour internal clock, leading to sleep disorders. Numerous studies have established that poor sleep, compared to healthy sleep patterns, significantly increases the risk of deteriorating cardiovascular system functions over time.

"To lessen the disease burden caused by environmental factors, such as light and air pollution, especially in densely populated and polluted areas globally, more effective regulations and preventive strategies must be developed," concludes Dr. Wang.